Unit 2.5
History: Preserving Works of Art Original version: Chemical methods are used to analyze
and preserve works of art. Non-destructive methods, such
as autoradiography and x-ray diffraction are used to study
the chemistry of paintings.
Video program cues: 30:55 - 35:40

“Albert Pinkham, a writer,
is famous for his use of images from the bible and Shakespeare.
One of the paintings that he has done which was checked
by autoradiography is the painting Jonah. It is a
scene depicting Jonah being swallowed by a whale. It was
interesting to us looking at it with autoradiography; we
were looking at it very carefully for 10-15 minutes, and
all of a sudden, one of the members of our group said: theres
a face in that autoradiograph... Its a portrait, one
painting was painted over another painting. And the portrait
painting was certainly not in the style of the writer.”

“X-ray fluorescence can
be used as a non-destructive technique for examining the
elemental composition of a painting. So by knowing the energy
of those X-rays, you can identify what that element is.
When taking an X-ray source and a painting, and you focus
the X-rays on the painting and the emitted X-rays can be
identified, and so you can identify the atom and have some
idea of what pigment it might be. If you find lead, for
example, from X-ray fluorescence, you cant be sure
which lead-containing pigment it is. So you may go on to
X-ray diffraction analysis. X-ray diffraction enables one
to identify a compound, not only the elements in the compound,
but the actual compound itself. It is very often a combination
of techniques. Thousands and thousands of years ago, earth
colors were used, in paintings in caves, for example. Those
same earth colors are still in use today in many cases.
But over time, there have been changes. For example, in
the 19th century, during the Industrial Revolution, many
pigments were manufactured. And today, a lot of pigments
that are used by artists are manufactured even discussing
how materials change in time by oxidation, or by cross-linking,
where small molecules combine with other molecules to form
larger molecules. That process is important for a conservator
for learning how things change with time. In order to do
that, you need to have a background in chemistry.”